Abstract : We report our new results of the magnetic field (B) morphologies toward W51 North, traced with the linear polarization of the dust continuum at wavelengths of 870 μm. The B morphologies are resolved with an angular resolution of typically 1'' using the Submillimeter Array (SMA). Dense structures with a number density 105 to 107 cm-3 are traced. In comparison, the B morphologies of sources at different evolutionary stages, from the collapsing core in W51 e2 (Tang et al. 2009a) and part of Orion BN/KL (Tang et al. 2010) to the ultra-compact HII region G5.89-0.39 (Tang et al. 2009b) clearly exhibit different morphologies, likely suggesting different roles of the B fields at different stages.